Collapsible self-erecting tubular frame structure and deployable electromagnetic reflector embodying same

ABSTRACT

A collapsible self-erecting three-dimensional frame structure constructed of relatively thin-walled resiliently flexible tubular frame members joined at their ends in a selected geometric configuration, such as a tetrahedral truss configuration, whereby the structure is collapsible, by flattening and folding the frame members, to a compact storage configuration wherein the frame members store elastic strain energy for effecting self-erection of the structure when the collapsing forces are removed. A deployable antenna reflector embodying the frame structure.

United States Patent [191 Williamson et al.

[ COLLAPSIBLE SELF-ERECTING TUBULAR FRAME STRUCTURE AND DEPLOYABLEELECTROMAGNETIC REFLECTOR EMBODYING SAME [75] Inventors: Clyde E.Williamson; Roy M. Acker,

both of Los Angeles; Gilbert A. Greenbaum, Encino; William J. Phillips,Gardena, all of Calif.

[73] Assignee: TRW Inc., Redondo Beach, Calif.

[22] Filed: May 23, 1973 [21] Appl. No.: 363,220

Related US. Application Data [63] Continuation of Ser. No. 131,218,April 5, 1971,

abandoned.

[52] US. Cl. 343/840; 52/646; 52/108; 343/897; 343/915 [51] Int. Cl E04h12/18 [58] Field of Search 52/108, 646; 343/840, 897, 343/915 [56]References Cited UNITED STATES PATENTS 1,545,129 7/1925 Cook 52/6483,221,464 12/1965 Miller 52/655 3,277,479 10/1966 Struble... 3,300,9101/1967 Isaac 3,434,254 3/1969 Rabin 3,564,789 2/1971 Vyvyan 52/108FOREIGN PATENTS OR APPLICATIONS 282,965 8/1949 Switzerland 52/655Primary ExaminerFrank L. Abbott Assistant Examinerl'lenry RaduazoAttorney, Agent, or FirmDaniel T. Anderson; Donald R. Nyhagen; Jerry A.Dinardo [57] ABSTRACT A collapsible self-erecting three-dimensionalframe structure constructed of relatively thin-walled resilientlyflexiblettubular frame members joined at their ends in a selectedgeometric configuration, such as a tetrahedral truss configuration,whereby the structure is collapsible, by flattening and folding theframe members, to a compact storage configuration wherein the framemembers store elastic strain energy for effecting self-erection of thestructure when the collapsing forces are removed. A deployable antennareflector embodying the frame structure.

1 Claim, 7 Drawing Figures U.S. Patent Oct. 14,1975 Sheet10f2 3,913,105

:9 Clyde EWHIicnmson 'Ro M. Acker Gil art A. Greenbaum WiHiClm J.Phillips INVENTORS ATTORNEY COLLAPSIBLE SELF-ERECTING TUBULAR FRAMESTRUCTURE AND DEPLOYABLE ELECTROMAGNETIC REFLECTOR EMBODYING SAlVIE Thisis a continuation of application Ser. No. 131,218 filed Apr. 5, 1971 nowabandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates generally to structures of the kind which are collapsible toreduced overall size for storage. More particularly, the inventionrelates to a three-dimensional collapsible frame structure of the classdescribed which is self-erecting under the force of elastic strainenergy stored within the collapsed structure. The invention relates alsoto a deployable antenna reflector embodying the frame structure.

2. Prior Art There is a continuing need for largetruss structures andthe like which can be collapsedfor stowage in greatly reduced volume andsubsequently deployed to envelop a volume or form planar, curved orcontoured surfaces for space or terrestrial uses. Large parabolicantennas which can be contracted to a small volume for stowage in aspace vehicle for launch into space orbit and then deployed are one suchexample. Maximum surface accuracy and minimum distortion due tomechanical loads and thermal gradients are fundamental requirements. Theultimate in design simplicity is also desired to insure deploymentreliability.

Many expandable structure concepts have been proposed to fulfill theseneeds. Inherent disadvantages, such as inability to maintain desiredaccuracy in operation, unreliable deployment, design and manufacturecomplexities, etc., have deterred acceptance. One such concept proposedfor space use, for example, is a truss reflector which exhibits goodstructural integrity and stability against thermal distortion, butpossesses extreme mechanical complexity and hence low deploymentreliability and high relative specific weight and cost. i

SUMMARY OF THE INVENTION The self-erecting collapsible structure of thepresent invention is constructed of a plurality of relatively slendertubular beams or frame members joined at their ends to form a unitaryframe structure which normally assumes a selected geometricconfiguration. These frame members are hollow, relatively thin-walled,resiliently flexible sleeves or tubes which are similar to those shownin Patent Nos. 3,217,328 and 3,434,254, and may be flattened and foldedto permit collapsing of the frame structure to a compact storageconfiguration. When thus flattened and folded, the tubular frame membersstore elastic strain energy which causes the members to spring back totheir original shape and thereby erect the frame structure to its normalgeometric configuration upon removal of the collapsing forces from thestructure.

The present frame structure may assume almost an infinite variety ofgeometric configurations. The particular frame structure disclosed is atetrahedral truss structure for use as a deployable antenna reflectorfor a spacecraft or the like. In this application, one face of the trussstructure has a generally parabolic curvature and carries anelectromagnetic reflective mesh which is foldable with the trussstructure for storage.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a perspective view of a tetrahedral truss structure accordingto the invention;

FIG. 2 is an enlarged fragmentary perspective view of one frame memberof the truss structure;

FIG. 3 is a section through the frame member illustrating the manner inwhich it may be flattened for folding;

FIG. 4 is an enlarged fragmentary plan view of one joint of the trussstructure;

FIG. 5 is an edge view of the joint looking in the direction of thearrow 5 in FIG. 4;

FIG. 6 is a perspective view on reduced scale of the truss structure inits collapsed configuration; and

FIG. 7 diagrammatically illustrates a preferred folding pattern of thetruss structure for collapsing it to its folded configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The collapsible self-erectingframe structure 10 selected for illustration in the drawings is atetrahedral truss structure for use as the supporting frame of adeployable spacecraft antenna reflector. This frame or truss structureis constructed of a plurality of relatively thin-walled resilientlyflexible tubular beams or frame members 12 similar to those disclosed inthe earlier mentioned patents. Frame members 12 are joined at their endsby connecting means 14 in a manner such that the structure normallyassumes its expanded configuration of FIG. 1. The structure iscollapsible to its conpact stowage configuration of FIG. 6 by flatteningand folding the frame members as described presently.

The illustrated frame or truss structure has a tetrahedral truss framewith opposing sides 16,18 which, in this instance, are generallyhexagonal in edge outline and are hereafter referred to as front andrear sides, respectively. The front frame side 16 has a generallyhexagonal perimeter P comprising a number of the frame members 12 joinedend to end by connecting means 14. Extending between and attached attheir ends to opposing connecting means at opposite sides of theperimeter and in oblique intersecting relation to one another are anumber of truss members T comprising frame members 12 joined end to endby connecting means 14 which also join the intersecting truss members toone another at their intersections.

The rear truss frame side 18 is similar to the front frame side and hasa generally hexagonal perimeter P and intersecting truss members Tcomprising frame members 12 joined end to end by connecting means 14.Truss members T are attached at their ends to the perimeter connectingmeans and are attached to one another at their intersections by theirconnecting means. Extending between and attached at their ends to theconnecting means 14 of the front and rear frame sides 16, 18 are framemembers 12 providing normal and diagonal connecting struts S which jointhe frame sides hedral configuration. These tetrahedral frame portionsare hereafter referred to as tetrahedral bays and have triangular facesin the front and rear frame sides l6, 18.

The frame members 12 of the truss structure are constructed of aresiliently flexible material, such as a heat treated plastic-like Mylaror Kapton, or metal, which is formed to the flanged tubular beamconfiguration illustrated in FIGS. 2 and 3. In this case, the framemembers are formed in two mating flanged sections whose flanges arejoined by stitching 19 to provide frame members or beams of the kinddisclosed in copending application Ser. No. 130,574, filed Apr. 2, 1971,under TRW Docket No. 4891, and entitled Strain Energy Erectile TubularBeam with Stitched Flanges. This resilient construction of the framemembers permits them to be flattened, as shown in broken lines in FIG.3, and then folded in such a way as to enable collapsing of the trussstructure to its storage configuration of' FIG. 6.

A significant feature of the illustrated truss structure resides in thefact that each intersection connecting means 14 must accommodate anumber of the frame members 12 which must hinge immediately adjacent theintersections. Some of the intersections, for example, such that shownin FIGS. 4 and 5, must accommodate six substantially coplanar framemembers and three diagonal frame members or struts S. This isaccomplished by using connecting means in the form of hexagonalplate-like fittings 28 and flattening the ends of the frame members andsecuring their flattened ends to the fittings with rivets 30 or thelike. The diagonal struts of each intersection are attached to theunderside of its connecting fitting. The flat pinched ends of the framemembers permits the latter to hinge freely on hinge axes adjacent andsubstantially coplanar with their respective connecting fittings. Thisis a significant feature of the design, since the frame members possessmaximum bending strength about axes normal to the planes of theconnecting fittings when either flattened or fully open. Hence, thetruss connecting fittings are stabilized in their normal orientationwhen the structure is either folded or deployed- The fold pattern forthe illustrated truss structure is diagrammatically illustrated in FIG.7 and involves folding or doubling the frame members 12 of the front andrear perimeters P P and truss members T F at their centers in inverted Vfashion. The diagonal truss members or struts S are not folded, butswing laterally inward in a manner similar to closing a camera tripod.This fold pattern provides the folded truss structure (FIG. 6) with anoverall diameter approximating the cumulative across flat dimensions ofthe individ ual hexagonal intersection fittings. In order to'furtherreduce packaged size, the frame members in the upper and lower surfacesmay be tapered toward their ends. This reduces the intersection fittingssize and also results in a truss member configuration which receivescolumn load more efficiently, being larger in diameter at its midpoint.

As noted earlier, the illustrated truss structure is the supportingframe of a deployable electromagnetic reflector for a spacecraft antennaor the like. The RF reflective surface of the antenna is provided by afoldable wire mesh 32 (shown in fragmentary fashion) fixed to the frontside 16 of the truss structure. This front side of thestructure'isprovided with the desired contour, in this instance aparabolic contour, by dimensioning the connecting struts S of thetrussstructure in such a way that the frame members 12 located in the planeof the. front side conform generally to, ie are tangent to, a.theoretical parabolic surface. Improved conformance of the front trussside to a parabolic surface may be ac complished in curving the framemembers of the front truss frame side 16. When the reflector is foldedto its storage configuration, the mesh 32 nests between the folded frontframe members, as shown in FIG. 7, and does not interfer withfolding ordeployment of the reflector.

An advantage of the illustrated antenna resides in the fact that itsopen construction achieves uniform exposure of virtually all parts ofthe structure to incident solar flux regardless of the orientation ofthe antenna relative to the sun.

I It will now be understood that the illustrated reflector iscollapsible to its compact stowage configuration of FIG. 6 by flatteningand folding of the frame members 12. When thus folded, the frame.members store elastic.

strain energy which causes self-erection or deployment of the reflectorto itsexpanded or deployed configuration of FIG. 1 when released. I

What is claimed as new in support of Letters Patent the like comprising:

a tetrahedral truss frame constructed of thin-walled,

resilient, collapsible, strain energy erectile tubular frame members andhaving two spaced and gener ally parallel frame sections formingopposite sides 1 of said frame and connecting struts between and joiningsaid frame sections;

each frame section having a perimeter comprising a number of saidtubular frame members joined end to end by first connectingmeans, andtruss members each comprising a number of :said tubular frame membersjoined end to end by second connecting means, said truss membersextending between opposite sides of said perimeter in obliqueintersecting relation to one another and being form with the tubularframe members of said frame sections a plurality of tetrahedral bays;each said tubular frame member having a tubular portion and coplanardimetrically opposed flanges along opposite sides of said tubularportion and the ends of the tubular portion of each frame member beingflattened into coplanar relation with its flanges; each said connectingmeans comprising a flat connecting plate located substantially in theplane of I the corresponding frame-section and seating the adjacentflattened frame member ends, each plate having an edge underlying theflattened end of and extending transverse to. each of the correspondingframe members, and means joining the member ends to their respectiveconnecting plates;

the outer side of one frame section conforming generally to an arcuatesurface of selected contour; such as a parabolic surface;

l. A deployable antenna reflector for spacecraft and i i and folded andsaid mesh being adapted to be folded with said frame members to permitcollapsing of said reflector to a compact storage configuration whcreinsaid frame members store elastic strain energy for deploying saidreflector when the collapsing force on the reflector is removed.

1. A deployable antenna reflector for spacecraft and the likecomprising: a tetrahedral truss frame constructed of thin-walled,resilient, collapsible, strain energy erectile tubular frame members andhaving two spaced and generally parallel frame sections forming oppositesides of said frame and connecting struts between and joining said framesections; each frame section having a perimeter comprising a number ofsaid tubular frame members joined end to end by first connecting means,and truss members each comprising a number of said tubular frame membersjoined end to end by second connecting means, said truss membersextending between opposite sides of said perimeter in obliqueintersecting relation to one another and being joined at their ends tosaid perimeter by said first connecting means and between their ends toone another at the truss member intersections by said second connectingmeans, and connecting struts comprising tubular frame members extendingbetween and joined at their ends by said connecting means to said framesections in such a way as to form with the tubular frame members of saidframe sections a plurality of tetrahedral bays; each said tubular framemember having a tubular portion and coplanar dimetrically opposedflanges along opposite sides of said tubular portion and the ends of thetubular portion of each frame member being flattened into coplanarrelation with its flanges; each said connecting means comprising a flatconnecting plate located substantially in the plane of the correspondingframe section and seating the adjacent flattened frame member ends, eachplate having an edge underlying the flattened end of and extendingtransverse to each of the corresponding frame members, and means joiningthe member ends to their respective connecting plates; the outer side ofone frame section conforming generally to an arcuate surface of selectedcontour, such as a parabolic surface; a flexible and foldableelectrically conductive mesh secured to said outer side of said oneframe section in a manner such that said mesh conforms generally to saidsurface contour to provide an electromagnetic reflecting surface whensaid truss frame occupies said tetrahedral truss configuration; and saidframe members being adapted to be flattened and folded and said meshbeing adapted to be folded with said frame members to permit collapsingof said reflector to a compact storage configuration wherein said framemembers store elastic strain energy for deploying said reflector whenthe collapsing force on the reflector is removed.